For some time now, high-pressure treatment is being used as a method for, among other things, inactivating microorganisms and certain enzymes in foodstuffs. The advantage of high-pressure treatment as compared with the more frequently used heat-treatment method is that the microorganisms and the degrading enzymes in the foodstuff are killed or inactivated without destroying vitamins and flavouring. During heat treatment, on the other hand, the taste and the vitamin contents are changed, which requires additives to restore, as far as possible, the nutritive value and taste of the substance.
During high-pressure treatment of, for example, foodstuffs, a so-called pressure intensifier is used. By pressure intensifier is meant here a device which has a high-pressure chamber in which the substance to be treated is pressurized. The pressurization can be accomplished, for example, by designing one of the end walls of the high-pressure chamber to accommodate a high-pressure piston with a certain area, which is insertable into the high-pressure chamber. Outside of the high-pressure chamber this piston is secured to a low-pressure piston with a larger area, arranged in a low-pressure chamber. By applying a certain pressure to the low-pressure piston, for example hydraulically, a higher pressure is thus obtained inside the high-pressure chamber. In high-pressure treatment of foodstuffs, it is common for the pressure in the high-pressure chamber to be set at about 1000-15000 bar.
The development of the technique for high-pressure treatment has led to two different, fundamental types of processes. According to one of these types, referred to here as the batch process, the high-pressure treatment is carried out in batches. In this case, the total amount of the substance to be treated is divided into batches, which are normally enclosed in a flexible package. When one batch is to be treated, the pressure intensifier is first opened and the batch is lifted into the cylinder member, whereafter the pressure intensifier is closed, and the high pressure is applied for a certain period of time. When the treatment is completed, the pressure intensifier is opened, the finished batch is removed from the cylinder member and a new batch can be placed therein. This process type is used above all for treatment of solid substances and other substances which cannot be transported in pipelines.
The other process type, here referred to as the semicontinuous process, is used above all for treatment of liquid substances which do not contain sensitive components. The substance to be treated is conducted in the pressure intensifier through a pipeline which is connected to the interior of the cylinder member via an inflow valve. When the inflow valve is opened, the cylinder member is filled with the substance. Then the inflow valve is closed and the high pressure applied. After the treatment, an outflow valve is opened, through which the treated substance is conducted to a pipe-line which is connected to the next stage in the process chain.
JP 1-171553 describes a device for high-pressure treatment according to the semicontinuous process. The device comprises a pressure intensifier with a high-pressure chamber. The high-pressure chamber is defined by a cylinder member and two confronting end members, a displaceable high-pressure piston extending through one of the end members. In the other end member, connection means for transporting the substance to and from the cylinder member are arranged. These connection means consist of an inflow valve and an outflow valve which communicate with an inflow channel and an outflow channel, respectively, extending through the other end member. Further, on the outside of the device the connection means are connected to lines which communicate with a storage tank and a product tank, respectively.
The substance which is treated is pumped from the storage tank via the inflow channel and the inflow valve into the cylinder member, whereby the outflow valve is closed. Thereafter, the inflow valve is closed and the substance in the high-pressure chamber is pressurized by displacing the high-pressure piston inwards in the chamber. After the pressure treatment, the pressure is reduced by displacing the high-pressure piston outwards in the high-pressure chamber. Thereafter, the outflow valve is opened and the high-pressure piston is again moved inwards in the cylinder member, the substance being pressed out of the high-pressure chamber through the outflow valve and the outflow channel and being forwarded via a pipe-line to the product tank.
Problems
High-pressure treatment according to the prior art described above involves problems. These problems are that, if the prior art is used for treating substances which contain components with a consistency different from that of the liquid, these components run the risk of being damaged. Such components, for example pieces of tomatoes, quenelles or pulp, are easily disintegrated by the shearing forces which arise in case of great flow rates. The disintegration is, of course, highly unwanted since it affects the natural consistency of the treated substance.
The flow rate in a valve or a line section depends on the flow and the flow area, such that the flow rate increases with a reduced flow area at a certain flow. Since the high-pressure treatment is normally included as one step in a manufacturing process, it is of the utmost importance that the total time of the high-pressure treatment is kept as short as possible. The time during which the substance is maintained under pressure cannot be reduced without deteriorating the treatment result. Therefore, the aim is instead to reduce the time for filling and emptying the cylinder member. This aim is achieved by increasing the flow when filling and emptying the cylinder member. During high-pressure treatment according to JP 1-171553 of substances containing sensitive components, however, large flows result in the sensitive components being damaged because of the high flow rates which arise in valves and lines which have a small flow area. Thus, to avoid damaging the treated substance, during high-pressure treatment according to this publication, the flow rates and hence the production rate must be kept low.
The problem with the prior art, described, inter alia, in JP 1-171553, thus resides in the fact that the valve members and channels of the connection means for transport of the substance cannot be designed with sufficiently large flow areas. The reasons for this are that the two valves and the connecting channels are designed in one and the same end member, and also that the valve members are adapted so as to open out inside the high-pressure chamber. Since both valves are located in one and the same end member, their total flow area is limited by the cross-section area of the cylinder member. For reasons of strength, the valve openings must be circular. This means that the theoretical geometrical limit to the maximum size of the flow area of a valve orifice, in relation to the cross-section area of the cylinder member, consists of the area of one of two equally large circles which are inscribed in a larger circle. Thus, theoretically, the flow area of a valve may, at a maximum, constitute one-fourth of the cross-section area of the cylinder member. In practice, however, the maximum permissible area is considerably smaller, which will be described below.
A proposal for a solution to the above problem is given according to the current technique by using only one valve both as inflow to and outflow from the cylinder member. For reasons of strength, however, this solution is not practicable at the high pressures used during high-pressure treatment of foodstuffs. In addition, the known solution entails other problems which render it unuseful for high-pressure treatment of foodstuffs. The substance which is treated is passed both into and out of the cylinder member via the same valve member and connection channel. Therefore, such untreated residues of the substance which adhere to these members on their way into the cylinder member will mix with the treated substance when the latter is on its way out. This means that bacteria and other microorganisms from the untreated substance can easily spread and, by propagation, pass on infection to the recently high-pressure treated substance. Such a solution, of course, is unacceptable when it comes to high-pressure treatment of foodstuffs.
However, a more serious limitation of the maximum flow area of the valve members is the fact that the valve members open out inside the high-pressure chamber. Because a pressure of up to 15000 bar prevails in the high-pressure chamber during the high-pressure treatment, it is in practice impossible, for reasons of strength, to design valve orifices and valve bodies which exhibit a larger pressure-exposed area than a few per cent of the cross-section area of the cylinder member.
In addition, according to the prior art described above, the connection channels which are arranged in the end member are, and must be, at least partially provided axially immediately outside that area of the end member which is pressure-exposed from the high-pressure chamber. In addition, these connection channels extend into the material zones in the end member in which the force flows from the high-pressure chamber are concentrated. The material around the channels is therefore subjected to considerable stresses and the larger the flow areas of the channels are made, the greater is the risk of cracks in the material in the end member. Admittedly, such designs are, according to the state of the art, the most suitable designs for transporting the substance to and from the high-pressure chamber. Still, they have obvious deficiencies. During high-pressure treatment of foodstuffs, pressures of up to 15,000 bar are utilized. These pressures approach the yield point of the very good structural steels which are used in the designs of the pressure intensifiers. It is thus necessary for the force-absorbing parts of the designs to be made very simple and without holes or cavities, which constitute notch factors. Such notch factors can multiply the stresses in the material in the vicinity of the cavities. This entails a considerable risk of material fractures, in particular when the stresses are cyclic and the cycle numbers are high, which is the case during high-pressure treatment of foodstuffs where a high treatment capacity is necessary.
Thus, according to the prior art described in the above document, it is, in practice, not possible to subject liquid substances, which contain sensitive components, to high-pressure treatment. In any case, it is not possible with an economically justifiable rate of treatment and without changing the natural consistency of the substance.
An alternative for high-pressure treatment of substances containing sensitive components would be to treat them according to the batch principle described above. In that case, transport of the substance through narrow conduits and valve members could be avoided. Owing to the slow and complicated handling of the batches, however, this alternative results in too low a rate of treatment, which leads to this mode of treatment being uneconomical when treating large quantities of the substance.
The object of the present invention is, therefore, to provide a device for high-pressure treatment of liquid substances, which allows large flows without the flow rates becoming too large or without the risk of an untreated substance being mixed with a treated substance.
The solution
The above object is achieved according to the present invention with a device of the kind described in the introductory part of the description and which is characterized in that the connection means are arranged outside the high-pressure chamber.
Since the connection means are located entirely outside the high-pressure chamber which is sealed by means of the high-pressure seals, no part of the connection means is subjected to the high pressures which prevail in the high-pressure chamber during pressurization of the substance. This, in turn, means that the valve members and channels which constitute the connection means can be dimensioned independently of the high pressures which prevail in the high-pressure chamber. Thus, the flow areas of these connection means can be chosen such that the substance can be transported with large flows, without the flow rate becoming so high that sensitive components in the substance run the risk of being damaged owing to shearing.
According to a preferred embodiment of the invention, the connection means for conducting the substance to and from the device are arranged, respectively, in the first and the second end member.
Since the substance is conducted to and from the high-pressure chamber, respectively, through an inlet and an outlet which are arranged in respective end members, it is possible to utilize large flow areas for all the flow channels which are passed by the substance on its way through the pressure intensifier. In actual fact, the device makes it possible for the cross section of the cylinder member alone to constitute an upper limit to the size of the smallest flow area. At the same time, the treated substance never has to be conducted through channels which may contain residues of non-treated substance. In this way, the risk of, for example, microorganisms from a non-treated substance coming into contact with, and infecting, a recently treated substance is thus eliminated.
In two further embodiments of the device according to the invention, the first one is characterized in that the connection means in the first end member comprise the first cylinder bore and at least one first connection channel which extends from this first cylinder bore to the outside of the device, and that the high-pressure piston is adapted to be displaced, as a valve member, past the orifice of the first connection channel in the cylinder bore. Further, the second embodiment is characterized in that the second end member comprises a plunger which is axially displaceable in a second axial cylinder bore which is provided in this second end member, that the connection means in the end member just mentioned comprise a second connection channel which extends from the second cylinder bore to the outside of the device, and that the plunger is adapted to be displaced, as a valve member, past the orifice of the second connection channel in the second cylinder bore.
The two embodiments described in the preceding paragraph allow the substance to be rapidly passed into or out of the cylinder member through the first and second end member, respectively, while at the same time the channels for transporting the substance are completely relieved of pressure also when the extremely high treatment pressure prevails inside the high-pressure chamber.
According to still another embodiment of the invention, low-pressure seals are arranged in the first and second cylinder bores, these low-pressure seals cooperating with the high-pressure piston and with the plunger, respectively, outside the orifices of the first and second connection channels, respectively, in the respective cylinder bore.
The low-pressure seals according to the above embodiment prevent the substance from leaking out of the device during filling and emptying of the cylinder member, and at the same time these seals prevent impurities from outside from penetrating into the device and mixing with the substance.
Further, another embodiment is characterized in that a spacing block is movably arranged between the plunger in the second end member and a frame, which is intended to take up axial forces during pressurization of the substance. In the inserted position, the spacing block is adapted to prevent the plunger from moving outwards and, in the retracted position, to allow the plunger to be displaced outwards.
The above embodiment offers a simple way of taking up great axial forces which act on the plunger, without the use of large hydraulic cylinders, which would otherwise be necessary. At the same time, simple and rapid opening and closing of the plunger are ensured, for example for filling or emptying the cylinder member.
Yet another embodiment of the invention is characterized in that the first and second connection channels each open out into an annular slot which is provided in the respective cylinder bore. This embodiment allows the cross-section area of the orifices of the connection channels in the cylinder bores to be increased and the substance to be moved more rapidly into and out of the cylinder member.
Further, two embodiments of the invention are intended to offer a fast and simple emptying of the cylinder member. According to one of these embodiments, the longitudinal axis of the cylinder member is inclined in relation to the horizontal plane, such that the end member which comprises the connection means which are intended to conduct the substance from the cylinder member is located at a lower level than the opposite end member. In this way, the substance is able to run out of the cylinder member by force of gravity during emptying. The second one of these embodiments is characterized in that the device is provided with means to introduce gas under pressure in the cylinder element. These means allow the time for emptying the cylinder member to be further reduced.